364 VICTOR E. SHELFORD. 



case above. In 1907 we attempted to point out possible relations 

 of succession and isolation, to adaptations to strata. 1 



Turning to the tiger beetles to illustrate a mode of analysis of 

 adaptation characters, we note that the entire family of Cicin- 

 delidse is characterized by the same general type of mouth parts, 

 same type of larvae (R. Shelford, '07; V. E. Shelford, '08). Ovi- 

 positors, feet, and larval structures are somewhat different in 

 the arboreal and terrestrial forms. The arboreal mode of life 

 occurs at least so far as the adults are concerned, to a greater or 

 less extent in each of the great tribes (Horn, '08, '10). The 

 genera Collyris (Horn, '08, p. 99), Pogonostoma (I. c.,p. 86), and 

 Ctenostoma (1. c., p. 89) are quite generally arboreal (Horn, '08, 

 '10). While the mode of origin of existing arboreal habits must 

 remain a matter of conjecture from which we cannot hope to 

 eliminate elements of subjective fancy, and while it is probable 

 that representatives of arboreal groups have become terrestrial 

 and vice versa, still the ground inhabitants are by far the most 

 numerous and most like other Coleoptera. The differences be- 

 tween ground forms and ectophytic forms are clearly more ele- 

 mentary than such characters as mouth parts, general larval or 

 ovipositor characters, because the former consist of minor modi- 

 fications of these general characters. If the problem of adapta- 

 tion may be attacked directly at all, we must first separate the 

 smaller from the larger adaptation characters. This accom- 

 plished we must note the kinds of conditions to which the 

 adaptation characters are related. In the case of the tiger 

 beetles, as will be found to be true in many other cases, the more 

 elementary characters are adaptations to stratum. 



As succession proceeds, as we have noted in the preceding 

 paper ('I2 1 ), conditions become progressively less favorable on 

 the ground, for many animals, and the terrestrial members of 

 the various groups give way to ectophytic forms of higher and 

 higher levels. We have already noted that the process of pene- 

 planation in the deciduous forest climate causes isolation of 

 uplands with oak hickory forest, which finally give way to beech 

 and maple (Cowles 1 unpublished observation). Thus the organ- 

 isms of such a habitat are subject to increasingly greater degrees 



1 Address before the American Society of Zoologists, December, 1907. 



